Organic Weed Control: Scientists Serve Up Mustard Meal To Tame Weeds

Agronomist Rick Boydston, with the ARS Vegetable and Forage Crops Research Unit in Prosser, Wash., is conducting the studies with plant physiologist Steven Vaughn, at the ARS National Center for Agricultural Utilization Research in Peoria, Ill. They evaluated the effects of three mustard seed application rates: half a ton, one ton and two tons per acre. Of the three, the one-ton and two-ton rates worked best in peppermint, reducing barnyard grass, green foxtail, common lambsquarters, henbit and redroot pigweed populations by 90 percent several weeks after application.

Although young peppermint plants sustained minor damage from the treatment early on, they recovered and resumed their normal growth. Onions weren't so lucky. Regardless of the application rate used, the treatment severely damaged the bulb crop when applied before emergence, or before the onions produced two true leaves. Applications at the two-leaf stage or later were more promising.

In trials with potted rose, phlox, coreopsis and pasque flower, the treatment killed or reduced the growth of annual bluegrass, common chickweed, creeping woodsorrel and liverwort. In treated plots, 86 to 98 percent of common chickweed seedlings died; those that survived were shorter and weighed less than treatment-free chickweed seedlings.

Besides white mustard, the researchers also evaluated the weed-control effects of field pennycress seed meal and dried distiller grains (DDGs), derived from corn ethanol production. Like white mustard, field pennycress also has potential as a biodiesel crop. It and the DDGs were less effective than white mustard at controlling weeds.

The research aim is three-fold: provide organic farmers with an alternative to hand-pulling, burning and other laborious methods of weed control in specialty crops including peppermint and potted ornamentals; develop value-added uses for seed meal, should mustards prove useful in making biodiesel; and diminish environmental risks possibly resulting from conventional herbicide use.